Electric wave circuits



Feb. 27, 1945. BARNEY ELECTRIC WAVE CIRCUIT Filed July 22, 1942 .R m w m w I E &E\ \n i A 33? ,3 2 LE .2 M1,. mm czl I mm I G N H mm m w H 0 m w NEGATIVE RES/STANCE CIRCUIT Patented Feb. 27, 1945 ELECTRIC WAVE CIRCUITS Harold L. Barney, Madison, N. 5., assignor to Bell Telephone Laboratories, Incorporated, New York, N. 3L, a corporation of New York Appiication duly 22, 1942, Serial No. 451,927

3 (Claims.

This invention relates to electric wave circuits and more particularly to an electronic device circuit including a vacuum tube of the secondary electron emission type.

An object of this invention is to so interconnect the various elements of the circuit as to produce an effective and stable negative resistance device.

A further object of the invention is to apply this negative resistance device to various useful purposes in a manner to be hereinafter described.

In accordance with this invention these objects are realized by the use of an electronic device comprising an electron source or cathode, a primary anode, an input control electrode or grid, a secondary electron emitting electrode adapted to emit secondary electrons in a ratio greater than unity when bombarded with electrons from the primary electron source, and a secondary electron collecting electrode. This device is associated with certain sources of potential and certain circuit elements to give the desired negative resistance.

A more complete understanding of this invention will be obtained from the following specification read with reference to the figures of the accompanying drawing wherein:

Fig. 1 shows in cross section one form of a vacuum tube especially adapted for the purpose of my invention;

Fig. 2 shows one circuit connection with such a device to produce a negative resistance circuit:

and

Figs. 3 to 8 show various applications of the negative resistance circuit.

While the electronic device for producing the results which are desired may take on various forms, Fig. 1 shows one form of tube which I find particularly well suited. This tube is described in detail in the copending application of A. M. Skellett, Serial No. 321,852, filed March 2, 1940 issued as Patent No. 2,293,177 dated August 18, 1942, and will herein be described briefly only, inasmuch as it represents but one type of tube with which to carry out my invention. In the said Fig. 1 there is shown at l a primary electron source or cathode. Surrounding this cathode is an anode 2. Between these two there is a grid 3 is a deflecting plate 1 which diverts the stream of electrons to a-secondary or floating anode 9. This anode has its surface so treated that it is a ready emitter of secondary electrons. Near to and in front of the anode 9 is a. collector grid 8. A shield .10 is preferably provided so positioned, as shown, to prevent the flow of electrons in undesired directions.

Fig. 2 shows one circuit arrangement yielding a two-terminal negative resistance circuit. In this circuit the primary anode 2 and the collector grid 8 are connected directly to the positive terminal of the potential source B1. The secondary anode 9 is connected at H to a point of intermediate potential, such as that on a bleeder circuit comprising resistances T1 and r2. Included between the secondary anode 9 and the point II is a resistance 1'3 of relatively high value and shunted around this resistance is an alternating current circuit comprising the condenser 01 and the primary l3 of a transformer T1. The control grid is shown as being connected to the cathode through'a biasing battery B2.

With appropriate values of potentials and element constants there will appear across the terminals A, B of the secondary [4 a negative resistance and as such this circuit constitutes a .part of my invention.

B1=135 volts 12:20pm) ohms B2=9 volts Ts==60,000 ohms r1=10,000 ohms C1=1 microfarad Transformer impedance ratio 75,000 to 600 Under these circumstances the resistance 'of the circuit looking into the terminals A, B was of the order of ohms.

Fig. 3 shows an application of this negative resistance circuit used as an amplifier in a 600 ohm line. Its insertion is equivalent to the reduction of the resistance of the circuit by 1100 ohms. Thus, when this negative resistance was placed in series with one side of the 600-ohm line it inserted a gain of approximately 21 decibels to either. direction of transmission.

Since the circuit of Fig. 2 yields a negative resistance, it is obviously possible to obtain a zero resistance by adjustment of the circuit or simply it would block transmission and this eflective short circuit would be under control of the confor a given control grid potential that the resistance of the tube circuit as seen looking in from the line is zero. If the control grid were made so negative that no electrons could get to the secondary anode, the impedance seen at the output of the negative resistance circuit, instead of being 1100 ohms, would be a large positive reactive value, depending on the. characteristics of the output transformer. This positive reactive value is sufilciently high so that it would introduce substantially no loss on the transmission line.

In Fig. 5 is shown a series control of transmission in which the impedance introduced in series withthe line may be made positive, negative or zero by varying the potential of the control grid of the tube. Thus, this switching amplifier may be made to introduce a gain or a loss according to the control grid bias. Applications of these types of switching amplifiers may be made to ""echo suppressors and other types of switching and suppressing devices.

It is to be noted that one of the characteristics of the circuit described in Fig. 2 is that voltage variations on the secondary anode 9 are 180 degrees out of phase with those on the conventional or primary anode 2. By virtue of this, certain other useful applications may be made. One of these is illustrated in Fig. 6which is a phase,

inverter and amplifier stage of a design to couple between a single-sided and a push-pull vacuum tube stage. In this circuit, as in Fig. 3, the collector grid 8 is shown connected directly to the positive terminal of the potential source B1. The primary anode is connected to this same potential point through a resistance 1'10. The secondary or floating anode 9 is connected through a resistance m to an intermediate potential point between the resistances rm and m.

In this circuit if the control grid 3 goes more positive, then anode 2 falls in potential but the anode 9 rises in potential. The points l6, 11 may therefore be connected directly as shown in Fig. 6 to the control grids of a push-pull circuit comprising two amplifying tubes, here shown as triodes. Biasing batteries B3 and B4 would normally be introduced to offset direct current potentials between the points l6, l1. In'view of the fact that the current variations through resistances m and m are not the same as those through 1'10 it would be necessary to give m+rn a different value from rm.

As a further concrete example of values appropriate for a particular tube to which reference has been made, the following constants are re- In the circuit with these constants, the alternating current voltages to ground from the two andensers or transformers involved in this circuit the frequency range over which it will operate extends from direct current to the frequency at which parasitic capacitances in the tube become limiting. For this circuit the grid batteries B: and 134 would not be the same in voltage since the direct current potentials to ground of the output leads from the first tube are not necessarily equal, although the alternating current potentials to ground are balanced.

Instead of the direct current coupling to the push-pull circuit of Fig. 6 it is obvious that a condenser coupling may be used as indicated in the circuit of Fig. 6A, this circuit being substituted at z Another circuit in which I make use ,of the negative resistance characteristic of my circuit and the opposite potential phasing of the primary and secondary anodes is shown in Fig. 7. Here an input circuit is shown as connected through the transformer T2 to the input circuit of the tube. The collector .grid is again connected to positive of battery. The primary anode 2 is connected to battery through a load circuit comprising the primary of transformer Ta. The secondary or floating anode 9 is connected through a resistance r: to an intermediate potential point determined by resistances n and 12. A feedback path comprising condenser C2 connects from the floating anode to the control grid. In view of the fact that the potential variations on the anode 9 are 180 degrees out of phase with those of anode 2, this feedback path gives positive feedback or regeneration.

vThe following circuit constants illustrate appropriate values to use in connection with the particular type of tube shown:

B1=135 volts n=2o,ooo ohms B2=5 volts ra=60,000 ohms r1=l0,000 ohms C2=8 microfarads With the constants as given the input and outodes are equal and, therefore, the alternating put impedances in one instance were 600 ohms and the over-all gain between 600 ohms sending and receiving circuits was 10.2 decibels. If the circuit between points 0-0 and D-D' is considered as the equivalent of a conventional vacuum tube circuitwithout feedback, its transfer conductance GM and its amplification factor a are 7500 micromhos and 8.9, respectively. The GM and a of the triode section of the tube with the feedback from the floating grid are 820 micromhos and 10.9, respectively, the same triode plate current of 4 milliamperes being used in both instances. The internal resistance ro of the triode part of the tube under the former condition was 13,300 ohms. The application of the regenerative feedback reduced the effective 7'0 of the triode plate circuit from 13,300 ohms to 1,000 ohms. It is of interest to note that in order to obtain a 600-ohm input impedance for the amplifier of Fig. '7, a resistance mwhich in the particular case referred to took on a value of 460 ohms, had to be shunted across the input terminals of the primary of transformer T2. This arises because of the fact that through the condenser coupling ity coupling from a preceding screen grid tube secondary anode, a source of potential with the V1. The feedback from the floating anode again effectively results in a negative resistance being shunted across the resistance 18, the feedback connection including condenser C2 and resistance R2. Thus the plate load impedance on V1 is greater than simply that of Ta and m in parallel,

being in fact the resultant of a negative resistance in shunt with T8 and 1'0. Therefore the resistances 1s and r9 may be made comparatively low with correspondingly small direct current voltage drop due to 1'8 while the alternating current plate load impedance of V1 may be made so high as to obtain maximum voltage amplification from the first stage.

While I have described certain applications of my negative resistance circuit it is to be understood that these are for illustrative purposes only and many variations may be made therein with-i out departing from the spirit of my invention.- What is claimedis: 1. A high vacuum tube circuit possessing negative resistance properties over a portion of its characteristic, the vacuum tube comprising a cathode and a primary anode, a control grid be tween the cathode and the primary anode, a secondary anode adapted to receive a lim ted number of primary electrons from the cathode, a collector grid adjacent the secondary anode and adapted to receive secondary electrons from the negative terminal connected to the cathode and thepositive terminal connected to the collector grid, a load circuit from the primary anode to a positive point on the potential source, a connection from the secondaryan'ode through a'resistance to an intermediate potential point with respect to the cathode, the potential being so ad-- justed that the volt-ampere characteristic from cathode to secondary-anode has anegative slope over its operating range, means for impressing a signal to be amplified between the control grid and the cathode, and a regenerative feedback connection consisting of an impedance connected from the secondarv anode to the control grid.-

2. The combination of" claim 1 characterized by the fact that the feedback connection comprises a condenser.

3. The combination of claim 1 characterized by the fact that the input circuit is coupled toa, precedingamplifier circuit through a resistance coupling, the direct current resistance load of the said preceding tube being held to a relatively 

